1. Field of the Invention
The invention relates to a cooling system. More particularly, the invention relates to a cooling system that is capable of cooling a heat source using a vapor compression refrigeration cycle.
2. Description of Related Art
In recent years, hybrid vehicles, fuel cell vehicles, and electric vehicles and the like that run using the driving force of an electric motor have become attractive as a way to address environmental concerns. In these types of vehicles, electrical equipment such as a motor, generator, inverter, converter, and battery generate heat by the sending and receiving electric power. Therefore, this electrical equipment must be cooled.
Japanese Patent Application Publication No. 2000-73763 (JP 2000-73763 A) describes a hybrid vehicle cooling system that includes a first cooling circuit that selectively or simultaneously cools an engine cylinder head and a driving motor, a second cooling circuit that cools an engine cylinder block, and a third cooling circuit that cools a power system control unit that drive-controls the driving motor.
The cooling system described in JP 2000-73763 A cools electrical system parts using a system that circulates coolant between a heat generating body and a radiator, similar to a normal vehicle that cools only an engine. In this kind of system, a radiator for cooling the electrical system parts must be newly provided, so mountability in a vehicle is poor.
Therefore, technology that cools a heat generating body using a vapor compression refrigeration cycle that is used for a vehicle air conditioning system has been proposed. For example, Japanese Patent Application Publication No. 2007-69733 (JP 2007-69733 A) describes a system that cools a heat generating body using refrigerant for an air conditioning system, and in which a heat exchanger that performs heat exchange with air for air conditioning, and a heat exchanger that performs heat exchange with the heat generating body, are arranged in parallel in a refrigerant passage that leads from an expansion valve to a compressor. Also, Japanese Patent Application Publication No. 2005-90862 (JP 2005-90862 A) describes a cooling system provided with heat generating body cooling means for cooling a heat generating body, in a bypass passage that bypasses a compressor, an evaporator, and a pressure reducer of an air conditioning refrigeration cycle.
With the cooling systems described in JP 2007-69733 A and JP 2005-90862 A, a cooling path for cooling a heat source such as electrical equipment is incorporated into a vapor compression refrigeration cycle, and when cooling the heat source, refrigerant in a two-phase gas-liquid state after passing through the pressure reducer is introduced into a refrigerant path that cools the heat source. Therefore, cooling performance for the heat source will become unstable if the amount of liquid-phase refrigerant decreases when a sudden load fluctuation occurs. Also, of the refrigerant in the two-phase gas-liquid state, the flowrate of the gas-phase refrigerant will become faster, so pressure loss as well as power consumption of the compressor for circulating the refrigerant will increase.